Important
One thing you can’t do with a petrol-driven or diesel-driven pressure washer is use it in an enclosed place because of the risk of carbon monoxide poisoning, so in those situations you employ the services of an electric pressure washer.

You can clean a lot of things with a pressure washer. It is a versatile piece of equipment.

Driveways: Tarmac
Concrete
Block Paved

Patios: Slabs
Decking
Furniture

Walls: Low walls
If you have an extendable pressure washing lance you’ll be able to clean higher walls.

Wooden Fencing

Drains : If you have a drain jetting kit.

Conservatories: You can only pressure wash the finery (spiky decorative stuff) at the top of the conservatory and the outside of the gutters. The roof panels will spring leaks if you try to pressure wash them.

Wheelie Bins

Car Valeting: A single phase electric model made by Kranzle will be sufficient as you won’t need a lot of power.

Graffiti: This will require a hot water system. You may also need to purchase some chemicals and a sandblasting kit to attach to your pressure washer.

Abattoirs/Farms: You’ll probably need an electric hot water system, as you’ll need hot water and some chemical additives to cut through the animal fats/grease.

Restaurants/Food Preparation Areas: Like with abattoirs you’ll most likely need a hot electric system. You also may choose to have a static machine that is attached to a wall  

Ship Hulls: For removing barnacles you’ll probably need a 500bar system.